This invention pertains to the art of pipe, tubing and conduits. More particularly, it pertains to conduits having a high strength to weight ratio such as corrugated plastic tubing.
The invention is particularly applicable to corrugated plastic drain tubing and will be described with particular reference thereto although it will be appreciated that the invention has much broader applications. For example, the inventive concepts are also deemed applicable to culverts, tunnels, subterranean conduits and the like.
Drainage tubing is conventionally used to remove excess surface and subsurface water from agricultural fields as well as from commercial and residential establishments. Generally, a trench is first dug in the soil by a trench digging machine, the drainage tubing positioned along the base of the trench and the trench is then backfilled. Water entering the tubing at one end and/or over the length thereof is carried to the other end for disposal.
Until recently, drainage tubing primarily comprised short lengths of cylindrical concrete or ceramic tiles. In laying these tiles along the base of the trench, they were typically spaced a small distance apart to provide a small gap for allowing water to enter into the tiles. This spacing was generally in the range of 1/4" or so. Shifting of the soil, however, often caused the tiles to become misaligned so that their effectiveness for their intended purpose was diminished. Further, such tile is heavy and cumbersome to handle and install. If heavy loads are applied, or if they are not bedded properly, individual ones of the tiles can break or shift and interrupt the water flow path.
In recent years, use of the individual concrete or ceramic tiles has been replaced by round or cylindrical corrugated plastic drainage tubing for many applications. Lengths of corrugated plastic tubing are fastened together at their ends to alleviate the aforementioned misalignment problems. Such tubing is usually perforated at spaced intervals therealong to allow water ingress and egress. The corrugated configuration generally provides the necessary tubing strength and rigidity, but forms troughs which collect sediment at the bottom or lower most areas thereof. Moreover, the round tubing shape defines a relatively large interior volume which undesirably tends to cause the tubing to fill the volume capacity of transporting vehicles without also filling their weight capacity. While corrugated plastic tubing constructions do not have the breakage problem associated with concrete or clay tile and have largely replaced such tile in many common applications, improper bedding of plastic tubing can result in excessive tubing deflection.
To reduce bulk for shipping, others have produced seamed tubing which is shipped flattened and assembled into its round or other shape just prior to installation. Such an arrangement is shown in, for example, U.S. Pat. No. 3,583,424. Others have attempted to develop collapsible tubing which is folded flat for storage and shipping purposes and then unfolded or opened for installation. Examples of such prior arrangement are shown in U.S. Pat. Nos. 3,343,567 and 3,508,587. However, both the seamed and collapsible tubing constructions have failed to meet with public acceptance for various reasons. Included among these reasons are high cost of manufacture, difficulty in assembling and handling, and a lack of structural strength particularly at the seams or hinges.
The present invention contemplates a structure or article which overcomes all of the above problems and others, and provides a new and improved arched conduit which is economical to manufacture, easy to ship, easy to handle, high in strength and which is readily adapted to use in a broad range of practical applications.